[test] more update to unittest2 api

[repo] properly mark object as saved once added to its source (code much probably gone during a merge...)

fix merge, some buffers weren't saved...

backport stable

[test] must now commit file creation since the later ValidationError trigger a rollback

cleanup and micro-optimization

[web action] has_editable_relations should not filter out final relations, fix regression introduced in 6358:22c95c5ef12d

[c-c] fix RuntimeError: 'maximum recursion depth exceeded while calling a Python object' we get when creating/upgrading/shelling an instance: hasattr() call __getattribute__, creating an infinite recursion error catched by the interpretor. Avoid this by testing the method is available on the class instead of the instance

[transaction] to avoid potential db corruption, we should rollback systematically in case of ValidationError

[selector] cleanup